a) Field of the Invention
This invention relates to artificial leather, and more specifically to artificial leather excellent in surface properties such as water repellency, oil resistance, abrasion resistance and non-tackiness in which a resin layer arranged on at least one side of a base sheet comprises a novel fluorine-containing polyurethane.
b) Description of the Related Art
Artificial Leather with a polyurethane layer arranged on at least one side of a base sheet such as a woven fabric or non-woven fabric has been used widely for many years. The polyurethane layer of such artificial leather is required to be excellent in stain resistance, waterproofness, abrasion resistance and non-tackiness, and depending on the application, is also required to be low in the coefficient of surface friction.
Polyurethane is obtained basically by reacting a palyol, a polyisocyanate and optionally, a chain extender, and depending on the kinds and combinations of these components, polyurethanes of various physical properties can be provided. It is to be noted that the term xe2x80x9cpolyurethanexe2x80x9d as used herein collectively means polyurethane, polyurea and polyurethane-polyurea.
Processes have been proposed to copolymerize an organic fluorine compound with such polyurethane to impart properties of the organic fluorine compound, such as water repellency and oil repellency, non-tackiness, abrasion resistance and stain resistance, while retaining the inherent good properties of the polyurethane.
For example, polyurethanes each of which is obtained by copolymerizing a one-end diol having a perfluoroalkyl group are proposed in JP S43-26518 B, JP S61-252220 A, etc.
As a conventional process for the preparation of a one-end diol (the term xe2x80x9cone-end diolxe2x80x9d as used herein means xe2x80x9ca compound having two hydroxyl groups at only one end of its moleculexe2x80x9d) having a perfluoroalkyl group (which, including a perfluoroalkenyl group, will hereinafter be abbreviated as xe2x80x9cthe Rf groupxe2x80x9d), a process which proceeds following such a reaction scheme as will be described next is known. 
As is appreciated from the foregoing, the conventional processes for the preparation of one-end diols having the Rf group all require many steps. High-purity products of the one-end diols having the Rf group are hence costly, so that these conventional processes have a problem in their-practical use on an industrial scale.
In polyurethanes each of which is available by copolymerizing a one-end diol having the Rf group as in the conventional art, on the other hand, any attempt to make the polyurethanes exhibit functions of fluorine by increasing the contents of fluorine in the polyurethanes leads to reductions in certain inherent properties of the polyurethanes such as rubber elasticity and mechanical strength and accordingly, results in artificial leather of inferior flexibility, softness and strength. Such an attempt is therefore not preferred.
This is attributed to properties of the Rf groups that the resulting polyurethane molecules are not easily bendable, are stiff and tend to orient in a particular direction, because fluorine atoms are very bulky and produce strong repulsion therebetween. As a result, a polyurethane is considered to be reduced in rubber elasticity due to inhibition to the freedom of the thermal motion of soft segments in the molecules and to be reduced in strength due to inhibition to aggregation of hard segments in the molecules. Namely, the above-described problem is considered to be caused for the reason that in a polyurethane, Rf groups derived from the conventional Rf-containing one-end diol give strong effects on the polyurethane backbone due to short distances between the Rf groups and the polyurethane backbone.
An object of the present invention is, therefore, to solve the above-described problems of the conventional art and hence, provide artificial leather composed of a polyurethane which is formed of an economical material and is excellent in water repellency and oil repellency, stain resistance, abrasion resistance, non-tackiness and the like.
The present inventors have proceeded with an extensive investigation to develop an economical process for the preparation of a one-end diol having an group, resulting in development of a novel preparation process. Further, the present inventors have also found that use of a fluorine-containing polyurethane, which employs the Rf-containing one-end diol available from the process, makes it possible to achieve the above-described object, leading to completion of the present invention.
The above-described object can be achieved by the present invention as will be described hereinafter.
In one aspect of the present invention, there is thus provided artificial leather having a base sheet and at least one resin layer arranged on at least one side of the base sheet, wherein the resin layer comprises a polyurethane having side chains derived from a fluorine-containing diol represented by the following formula (I): 
wherein Rf represents a perfluoroalkyl or perfluoroalkenyl group having 1 to 20 carbon atoms; X represents a substituted or unsubstituted alkylene group having 1 to 10 carbon atoms, a substituted or unsubstituted alkenylene group represented by xe2x80x94CHxe2x95x90CHxe2x80x94(CH2)nxe2x80x94 in which n stands for an integer of from 1 to 10, or 
in which n stands for an integer of from 0 to 6; Y represents a direct bond, xe2x80x94Oxe2x80x94, xe2x80x94NHxe2x80x94, or xe2x80x94R0xe2x80x94NHxe2x80x94 in which R0 is an alkylene group having 1 to 6 carbon atoms; Z represents a direct bond or xe2x80x94N(Rxe2x80x2)Rxe2x80x94 in which R is an alkylene group having 1 to 20 carbon atoms and Rxe2x80x2 is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms; R1 and R2 each independently represent a divalent organic group; and R3 represents a residual group of an aliphatic, alicyclic or aromatic diisocyanate.
Owing to the formation of the resin layer, which is arranged on the base sheet, with the fluorine-containing polyurethane containing Rfs in its side chains, the artificial leather according to the present invention is provided with excellent surface propertiesxe2x80x94such as water repellency and oil repellency, stain resistance, abrasion resistance and non-tackinessxe2x80x94along with the superb rubber elasticity and strength properties inherent to the polyurethane and the fluorine compound, respectively.
The present invention will next be described in further detail based on certain preferred embodiments. The artificial leather according to the present invention is characterized in that the polymer layer arranged on at least one side of the base sheet comprises the polyurethane having side chains derived from the fluorine-containing diol represented by the formula (I), that is, the Rf-containing one-end diol.
The polyurethane for use in the present invention can be obtained by a conventional process for the production of polyurethanes, namely, by reacting the Rf-containing one-end diol represented by the formula (1), an active-hydrogen-containing compound and a diisocyanate, optionally in the presence of a chain extender. The Rf groups in the polyurethane, said Rf groups being stiff and having strong orientation, are located at ends of side chains and are spaced at least a predetermined distance from the backbone. Moreover, the Rf groups are each bonded to the backbone of the polyurethane via a urethane bond or a urea bond, so that enhanced compatibility exists between the side chains and the polyurethane backbone and the freedom of motion of soft segments and the aggregation of hard segments in the polyurethane are not inhibited by the Rf groups. Accordingly, the use of the fluorine-containing polyurethane has made it possible to provide the artificial leather with excellent surface propertiesxe2x80x94such as water repellency and oil repellency, stain resistance, abrasion resistance and non-tackinessxe2x80x94along with the superb rubber elasticity and strength properties inherent to the polyurethane and the fluorine compound, respectively.
The Rf-containing one-end diol, which is employed for the production of the polyurethane for use in the present invention, can be prepared by the following steps:
a) Firstly, a fluorine-containing diol (1) having an active-hydrogen-containing group (for example, a hydroxyl group) and a diisocyanate (2) are reacted at an NCO/OH ratio of approximately 2 to obtain a fluorine-containing compound (3) having one free isocyanate group in its molecule.
b) Using a difference in the reactivity to an isocyanate group between an amino group and a hydroxyl group, the fluorine-containing compound (3) and a dialkanolamine (4) are then reacted at a temperature not higher than 50xc2x0 C. such that the isocyanate group and the amino group are selectively reacted to obtain an Rf-containing one-end diol represented by the following formula (A). 
wherein Rf, R1 to R3, X and Z have the same meanings as defined above, and Z0 represents H or an alkylamino group having 1 to 20 carbon atoms and a single primary or secondary amino group at an end thereof.
Examples of fluorine-containing compounds usable in the present invention can include the following compounds:
(1) Alcohol Type 
(2) Epoxy Type 
The above-described epoxy compounds are each used after introducing a terminal hydroxyl group therein by a reaction with an active-hydrogen-containing compound such as a polyol, a polyamide or a polycarboxylic acid.
(3) Amine Type 
(4) Carboxylic Acid Type 
The above-listed fluorine-containing compounds, each of which has an active-hydrogen-containing group, are examples of compounds preferred for use in the present invention, and in the present invention, the fluorine-containing compound shall not be limited to these exemplified ones. In the present invention, it is therefore possible to use not only the above-exemplified fluorine-containing compounds but also known fluorine-containing compounds presently sold on the market and available from the market. Fluorine-containing compounds particularly preferred in the present invention are the above-exemplified fluorine-containing compounds of the alcohol type.
As the diisocyanate for use in the present invention, any diisocyanate known to date is usable, and no particular limitation is imposed thereon. Preferred usable examples can include aromatic diisocyanates such as toluene-2,4-diisocyanate, 4-methoxy-1,3-phenylene diisocyanate, 4-isopropyl-1,3-phenylene diisocyanate, 4-chloro-1,3-phenylene diisocyanate, 4-butoxy-1,3-phenylene diisocyanate, 2,4-diisocyanatodiphenyl ether, 4,4xe2x80x2-methylenebis(phenyl-isocyanate) (MDI), durylene diisocyanate, tolidine diisocyanate, xylylene diisocyanate (XDI), 1,5-naphthalene diisocyanate, benzidine diisocyanate, o-nitrobenzidine diisocyanate, and 4,4-diisocyanatodibenzyl; aliphatic diisocyanates such as methylene diisocyanate, 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, and 1,10-decamethylene diisocyanate; alicyclic diisocyanates such as 1,4-cyclohexylene diisocyanate, 4,4-methylene-bis(cyclohexylisocyanate), 1,5-tetrahydronaphthalene diisocyanate, isophorone diisocyanate, hydrogenated MDI, and hydrogenated XDI; and obviously, polyurethane prepolymers obtained by reacting these diisocyanates with polyols or polyamines of low molecular weights such that the resulting prepolymers have isocyanate groups at ends thereof.
Examples of dialkanolamines usable in the present invention can include compounds represented by the following formula: 
wherein R1, R2 and Z0 have the same meanings as defined above, and preferably, R1 and R2 may each independently represent a divalent group having 2 to 12 carbon atoms and containing an aliphatic, alicyclic or aromatic ring, and the divalent group may contain one or more O, N and/or S atoms therein.
Preferred examples can include diethanolamine, dipropanolamine, dihexanolamine, 1-aminopropane glycol, diethanolaminomethylamine, diethanolaminoethylamine, and diethanolaminopropylamine.
A more specific description will now be made about the preparation process of the Rf-containing diol represented by the formula (I).
Firstly, the fluorine-containing compound, which has the active-hydrogen-containing group, and the diisocyanate are reacted at an equivalent ratio such that the reaction product contains one free isocyanate group in a molecule (NCO/OH≈2), in a solventless manner or in an organic solvent, in the presence or absence of a conventional polymerization catalyst for polyurethanes (for example, an organometal compound, a tertiary amine or the like), and at 0 to 150xc2x0 C., preferably 20 to 90xc2x0 C.
At a temperature of 50xc2x0 C. or lower, preferably 40xc2x0 C. or lower, more preferably 30xc2x0 C. or lower, the above-described fluorine-containing compound having one free isocyanate group is then added dropwise into the above-described dialkanolamine.
Under these conditions, an isocyanate group selectively reacts with an amino group before a hydroxyl group [Ann. Chem., 562, 205 (1949)], whereby an Rf-containing one-end diol represented by the formula (I) according to the present invention is obtained and at low temperatures, a portion of the reaction product progressively precipitates as crystals in an organic solvent as the reaction proceeds. After completion of the reaction, the reaction mixture is poured into a poor solvent such as water, toluene, xylene or n-hexane to cause precipitation of the reaction product as crystals.
Unreacted diisocyanate and dialkanolamine can be eliminated by washing the precipitated crystals with a poor solvent (an aromatic or aliphatic hydrocarbon) at room temperature. The Rf-containing one-end diol represented by the formula (I) can, therefore, be obtained with high purity.
The fluorine-containing polyurethane for use in the present invention can be obtained by reacting the Rf-containing diol, which is represented by the formula (I) and has been obtained by the above-described reaction, with the above-described diisocyanate and also with the diol and/or diamine.
As the diol, diols which have been used to date for the production of polyurethane are all usable, and no limitation is imposed thereon. Illustrative are glycols of low molecular weight such as ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butylene glycol, and 1,6-hexamethylene glycol; polyester diols obtained from dibasic acids, such as adipic acid, maleic acid and terephthalic acid, and glycols; polyester diols such as polylactones obtained by subjecting lactones to ring-opening polymerization with glycols; polycarbonate diols; and polyether diols such as polytetramethylene glycol, polyethylene glycol, and polypropylene glycol.
As the diamine, diamines which have been used to date for the production of polyurethane are all usable, and no particular limitation is imposed thereon. Illustrative are aliphatic diamines such as methylenediamine, ethylenediamine, trimethylenediamine, hexamethylenediamine, and octamethylenediamine; aromatic diamines such as phenylenediamine, 3,3xe2x80x2-dichloro-4,4xe2x80x2-diaminodiphenyl ether, 4,4xe2x80x2-methylenebis(phenyl)amine, 4,4xe2x80x2-diaminodiphenyl ether, and 4,4xe2x80x2-diaminodiphenylsulfone; and alicyclic diamines such as cyclopentadiamine and cyclohexyldiamine. Examples of the chain extender can include the above-described diols and diamines of low molecular weight. Chain extenders which have been used to date for the production of polyurethane are all usable, and no particular limitation is imposed thereon.
Using these components and a conventional process known for the production of polyurethane, the fluorine-contadining polyurethane according to the present invention can be obtained. The process according to the present invention for the production of polyurethane comprises reacting the, Rf-containing diol represented by the formula (I), the diisocyanate, the diol and/or diamine, and optionally, the chain extender. No particular limitation is imposed on the reaction conditions. Further, no particular limitation is imposed either on the reaction method, and the reaction can be performed by any method such as bulk polymerization, solution polymerization or dispersion polymerization. Moreover, a suitable combination of a diol, a diamine and a diisocyanate can be chosen depending on the application purpose and performance requirements of a target fluorine-containing polyurethane, and no particular limitation is imposed on them.
In the fluorine-containing polyurethane obtained by using the Rf-containing diol, the fluorine-containing side chains are bonded via R1 and R2 thereof to the backbone of the fluorine-containing polyurethane by means of urethane bonds (xe2x80x94NHxe2x80x94COxe2x80x94Oxe2x80x94) and/or urea bonds (NHxe2x80x94COxe2x80x94NHxe2x80x94). Use of a diol provides a polyurethane, use of a diamine provides a polyurea, and combined use of a diol and an amine provides a polyurethane-polyurea.
The content of the fluorine-containing side chains in the polyurethane molecule may preferably range from 3 to 80 wt. % in terms of a fluorine content based on Rf groups in the polyurethane molecule. A content lower than 3 wt. % leads to insufficient development of a function associated with surface energy based on the Rf groups, while a content higher than 80 wt. % results in reductions in good properties inherent to polyurethane such as abrasion resistance and mechanical strength. Their contents outside the above-described range are, therefore, not preferred. Their content may preferably range from 5 to 50 wt. %, with a range of from 5 to 25 wt. % being more preferred.
As another embodiment of the present invention, the artificial leather is formed by using a fluorine-containing polyurethane which further contains polysiloxane segments, which have been derived from a polysiloxane having at least one active-hydrogen-containing group, in an amount such that the content of polysiloxane segments in the polyurethane molecule falls within a range of from 1 to 75 wt. %.
The polysiloxane for use in the present invention has at least one active-hydrogen-containing group, for example, at least one amino group, epoxy group, hydroxyl group, mercapto group, carboxyl group or like group. Preferred examples of such a polysiloxane can include the following compounds.
(1) Amino-modified Polysiloxanes 
(2) Epoxy-modified Polysiloxanes 
(3) Alcohol-modified Polysiloxanes 
(4) Mercapto-modified Polysiloxanes 
(5) Carboxyl-modified Siloxanes 
The above-listed polysiloxane, each of which has an active-hydrogen-containing group, are examples of compounds preferred for use in the present invention, and in the present invention, the siloxane shall not be limited to these exemplified compounds. Not only the above-exemplified polysiloxanes but also polysiloxanes presently sold on the market and readily available from the market are, therefore, all usable in the present invention. Polysiloxanes particularly preferred in the present invention are those containing at least one hydroxyl group or amino group.
The fluorine and silicon-containing polyurethane according to the present invention, which is available from the use of an Rf-containing one-end diol, a polysiloxane having at least one active-hydrogen-containing group in a molecule and the above-described another polyurethane component, is a polyurethane in which segments formed from a diisocyanate and segments formed from a diisocyanate are contained in the polyurethane backbone as in conventional polyurethanes, fluorine-containing side chains formed from a fluorine-containing diol presented by the formula (I) are bonded via R1 and R2 thereof to the backbone by means of urethane bonds and/or urea bonds, and polysiloxane segments formed from the polysiloxane are bonded to the backbone by means of urethane bonds and/or urea bonds.
The content of the polysiloxane segments in the polyurethane molecule may preferably be in such an amount that the siloxane content in the molecule ranges from 1 to 75 wt. %. A content lower than 1 wt. % leads to insufficient development of a function associated with surface energy based on the polysiloxane segments, while a content higher than 75 wt. % results in reductions in good properties inherent to polyurethane such as abrasion resistance and mechanical strength. Their contents outside the above-described range are, therefore, not preferred. Their content may preferably range from 3 to 50 wt. %, with a range of from 5 to 20 wt. % being more preferred.
For the production of such a fluorine-containing polyurethane of present invention as described above (the term xe2x80x9cfluorine-containing polyurethanexe2x80x9d as used herein will hereinafter mean to also embrace such compounds as containing polysiloxane segment(s)), the above-described polysiloxane can be used in the form of a solution in an organic solvent, a suspension in water, or pellets of 100 wt. % solid content.
The preferable fluorine content and polysiloxane segment content in the fluorine-containing polyurethane according to the present invention vary depending upon its application purpose, so that it is desired to obtain each fluorine-containing polyurethane with fluorine and polysiloxane segment contents suited for its application purpose.
The weight average molecular weight of the fluorine-containing polyurethane according to the present invention (as measured by GPC and calibrated against standard polystyrene) may range preferably from 5,000 to 500,000, more preferably from 30,000 to 150,000.
In the artificial leather according to the present invention, the resin layer formed of the above-described fluorine-containing polyurethane is formed on at least one side of the base sheet. No particular limitation is imposed on the base sheet, and base sheets which have been used for the production of artificial leather to date are all usable. Illustrative are woven various fabrics and non-woven fabrics, those obtained by impregnating such fabrics with resins, and those obtained by forming porous layers on their surfaces.
Upon producing the artificial leather according to the present invention, the resin layer made of the fluorine-containing polyurethane is formed on at least one side of the base sheet, and no particular limitation is imposed on the process for its formation. Preferred examples of the formation process can include: a process which comprises preparing a coating formulation by using, as an essential component, the fluorine-containing polyurethane useful in the present invention and adding various additives, such as conventionally-known coloring matters, plasticizers, surfactants, age resisters, crosslinking agents, as needed, coating the coating formulation onto a surface of the base sheet or impregnating the base sheet with the coating formulation, and then drying the thus-applied coating formulation to form the resin layer; a process which comprises coating the coating formulation onto a sheet of release paper, drying the coating formulation to form a film, and subsequent to peeling, bonding the film onto the base sheet; a process which comprises forming the fluorine-containing polyurethane into a film by calendering or a like method, and then bonding the film onto the base sheet. The fluorine-containing polyurethane layer may be of any thickness, but generally, has a thickness of from about 0.1 to 100 xcexcm or so. The artificial leather according to the present invention can include one available by arranging a layer, such as a layer of a vinyl chloride resin with a plasticizer incorporated therein, and then forming the above-described fluorine-containing polyurethane layer as a stain-resistant layer over the vinyl chloride resin layer.
Artificial leather according to the present invention, which can be obtained as described above, has excellent stain resistance, waterproofness, abrasion resistance and non-tackiness, and therefore, can be used for the production of clothing, sportswear, furniture, wall paper, cars, shoes, sports shoes, gloves, tents, sheets, footwear, miscellaneous goods, and the like.